This invention relates to a flexible sheet suitable as important stock material for disposable sanitary articles, particularly for disposable body fluid absorbent sanitary articles such as disposable diapers or sanitary napkins.
FIG. 6 in the accompanying drawings is a perspective view showing a soft touch exhibiting microapertured plastic sheet 110 disclosed by Japanese Patent Application Disclosure No. 1987-57551. This plastic sheet 110 is adapted to be used as both the top- and backsheets of disposable diapers and is made by feeding a relatively thin unprocessed plastic sheet onto a wire-mesh belt and is then processing the sheet with high pressure liquid jet streams.
The microapertured plastic sheet 110 is formed on its surface destined to be placed against a wearer""s skin with a plurality of cylindrical projections 120 which are formed, in turn, on their tops with microapertures 125. The periheraledge of the microapertures 125 are fringed like petals. The sheet 110 is described as exhibiting a cloth-like touch and a lusterless appearance.
In general, a soft touch exhibited by the plastic sheet used in disposable diapers or sanitary napkins when the sheet comes in contact with the wearer""s skin is evaluated on the basis of the soft touch exhibited by woven or nonwoven fabrics made of natural or synthetic fiber.
Taking account of the fact that the plastic sheet of prior art has the cylindrical projections formed at their tops with the microapertures which are fringed along their peripheral edges like petals, certainly a cloth-like soft touch will be obtained as the wearer""s skin moves to rub the fringed peripheral edges. However, the cylindrical projections themselves have a stiffness substantially higher than a stiffness of the fringed peripheral edges and it is apprehended that the sheet might be even stiffened rather than being softened by forming the sheet with a plurality of such cylindrical projections. Therefore, it is not easy for the plastic sheet of prior art to exhibit a high softness as offered by woven or nonwoven fabrics.
While the plastic sheet of prior art is described as exhibiting a lusterless appearance since the peripheral edges of the respective microapertures are fringed like petals, outer peripheral surfaces of the cylindrical projections 120 as well as the flat zones defined between each pair of the adjacent cylindrical projections 120, 120 are serious factor that enhance the lustrous appearance of the sheet 110.
An object of this invention is to provide a flexible sheet used for disposable sanitary articles that exhibits a comfortably soft touch, on one hand, and a surface appearance in which luster is sufficiently alleviated.
According to this invention, there is provided a flexible sheet for a disposable sanitary article. The flexible sheet is made of flexible plastic sheet having top and bottom surfaces and a thickness of 0.001xcx9c0.05 mm, said flexible sheet including a plurality of substantially plane regions extending in parallel one to another in one direction each having a width of 0.03xcx9c1 mm and a plurality of aperture-arrays intermittently arranged in the one direction, each lying between each pair of the adjacent aperture-arrays, each of the aperture-arrays including a plurality of individual apertures each having a width of 0.07xcx9c1 mm and a length corresponding to 1.5 or more times of the width so that the plane regions and the aperture-arrays are alternatively arranged in the direction orthogonal to the one direction. Each pair of adjacent the aperture regions having the aperture-array therebetween are connected to each other by a plurality of bridge regions extending from these adjacent plane regions across the aperture-array. Each of the plane regions is provided at least along a part of its zone defining the apertures extending in the one direction with a plurality of regions rising on a top surface of the sheet so as to form a substantially irregular undulation and a plurality of trough regions each defined between each pair of adjacent the rising regions in the one direction wherein, of the rising regions formed on the flexible sheet, the rising regions defining on both sides thereof the trough regions each having a depth of at least 0.01 mm are distributed at a density of at least 500/cm2.
The flexible sheet according to this invention is provided with a plurality of the aperture-arrays extending in one direction and provided on its upper side with a plurality of the fine and easily deformable rising regions irregularly undulating along the peripheral edges of the respective aperture-arrays at a density of at least 500 rising regions per 1 cm2 so that each of the rising regions defines on its both sides the trough regions having a depth of at least 0.01 mm, respectively. The rising regions distributed at such high density on its upper side give the top surface of the flexible sheet a soft comfortable touch and make the sheet lusterless. These rising regions are effective also to improve the water repellency of the sheet""s top surface.